Reinforced Rampdown For Composite Structural Member And Method For Same

ABSTRACT

A composite member with a reinforced rampdown or taper has a composite noodle bonded to an end of a core to fill the taper.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/065,350, filed Feb. 24, 2005, which is hereby incorporated herein inits entirety by reference.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The research underlying this invention was supported in part with fundsfrom the U.S. Air Force grant no. F33615-98-3-5103. The United StatesGovernment may have an interest in the subject matter of this invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the formation of composite structuralmembers and, more particularly, relates to a composite structural memberhaving a support member with a core between laminate sheets.

2. Description of Related Art

A sandwich panel is formed of a core that is sandwiched betweencomposite laminate sheets. The laminate sheets can be formed of variousconventional composite materials using any of various methods. Forexample, the sheets can be formed by disposing preimpregnated pliesaround the core and consolidating and curing the plies. The core can bea lightweight honeycomb or foam to provide high strength and/orstiffness with relatively low weight.

The core of such a composite member typically has a substantiallyuniform thickness throughout except at the ends, where the core definesa rampdown or taper in the composite member. The tapered edge defines atransition between the core and a peripheral portion where the laminatesheets are joined directly together without the core. The taperedportion is relatively weak. Therefore, additional plies can be added inthe tapered region to reinforce the region. These additional pliesincrease the weight, time for manufacture, and cost the panels.

SUMMARY OF THE INVENTION

The present invention provides a composite member such as a sandwichpanel with a reinforced rampdown or tapered portion. The tapered portionis reinforced by adding a laminate support member at the apex of thecore taper.

According to one embodiment, the composite member includes first andsecond laminate sheets that define opposite sides of the compositemember. A core and a laminate support member are disposed in a spacedefined between the two sheets. The core can be formed of a honeycombmaterial or foam, and the laminate member can be formed of a pluralityof layers of composite material, such as plies disposed in alternatedirections. In particular, the support member is disposed proximate thecore in a tapering portion of the space where the sheets are angledtogether. Thus, the support member supports the composite member. Forexample, the sheets can be substantially parallel in a first portion ofthe member, with the core disposed between the sheets. At an edge of thecore, the sheets can be angled together to define the tapering portion,with the support member disposed between the sheets in the taperingportion. Beyond the tapered portion, i.e., opposite the tapering portionfrom the first portion, the composite member can define a second portionin which the sheets are in contact. The support member can be adjacentthe core and joined to the core by an adhesive. The support member candefine a triangular cross-sectional shape that corresponds to thetapering portion of the space between the first and second sheets. Insome cases, the core can also define a partially tapering portion thatcorresponds to the tapering portion of the space.

The present invention also provides a method of forming a compositemember. The method includes providing the core and laminate supportmember between the first and second laminate sheets. The support membercan be cured before assembly with the sheets, or the support member canbe disposed in an uncured condition and then cured between the sheets,e.g., while also curing the sheets. In any case, the support member canbe formed of layers of composite material, which can include pliesdisposed in alternate directions.

The sheets can be joined at a position opposite the support member fromthe core, and the support member can be joined to the core, e.g., with afoaming adhesive. In some cases, the core can be provided with atapering portion that defines a surface adjacent the support member.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate preferred and exemplary embodimentsand are not necessarily drawn to scale.

FIG. 1 is a section view illustrating a composite member.

FIG. 2 is a section view partially illustrating a composite member.

FIG. 3 is a section view partially illustrating another compositemember.

FIG. 4 is an expanded section view schematically illustrating the lay-upof the structural member.

FIG. 5 is an expanded section view schematically illustrating the lay-upof the support member.

FIG. 6 is an expanded perspective view schematically illustratingseveral of the layers of the support member.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully with reference tothe accompanying drawings, in which some, but not all embodiments of theinvention are shown. This invention may be embodied in many differentforms and should not be construed as limited to the embodiments setforth. Like numbers refer to like elements throughout.

A composite structural member 10 according to one embodiment of thepresent invention is shown in FIG. 1. The composite member 10 is asandwich panel that includes first and second laminate sheets 12, 14over a core 16. A laminate support member 20 is disposed between thesheets 12, 14 proximate to the core 16 at the end of its taper 22. Thetaper 22 defines a transition between a region 24 where the core 16 isdisposed between the sheets 12, 14, and a second region 26 where thesheets 12, 14 contact to form a coreless laminate. The support member 20is disposed where the sheets come together, a region that is susceptibleto cracking.

The sheets 12, 14 typically are fiber reinforced composite and may bewing panels for aircraft. Composite materials are further described inU.S. Pat. Nos. 6,562,436; 6,689,448; and 6,709,538, which areincorporated by reference.

The matrix material can be thermoplastic or thermoset polymeric resins.Exemplary thermosetting resins include allyls, alkyd polyesters,bismaleimides (BMI), epoxies, phenolic resins, polyesters, polyurethanes(PUR), polyurea-formaldehyde, cyanate ester, and vinyl ester resin.Exemplary thermoplastic resins include liquid-crystal polymers (LCP);fluoroplastics, including polytetrafluoroethylene (PTFE), fluorinatedethylene propylene (FEP), perfluoroalkoxy resin (PFA),polychlorotrifluoroethylene (PCTFE), andpolytetrafluoroethylene-perfluoromethylvinylether (MFA); ketone-basedresins, including polyetheretherketone (PEEK™, a trademark of VictrexPLC Corporation, Thorntons Cleveleys Lancashire, UK); polyamides such asnylon-6/6, 30% glass fiber; polyethersulfones (PES); polyamideimides(PAIS), polyethylenes (PE); polyester thermoplastics, includingpolybutylene terephthalate (PBT), polyethylene terephthalate (PET), andpoly(phenylene terephthalates); polysulfones (PSU); or poly(phenylenesulfides) (PPS).

The materials used for the composite structural member 10 can beselected, at least in part, according to the intended use of the member10, as a structural panel for an aircraft, or other aerospacestructures, automobiles, marine vehicles, other vehicles, buildings andother structures, and the like.

The core 16 is lightweight such as honeycomb made from aluminum, othermetals, fiberglass-reinforced phenolic or other resin, resin-coatedpaper, or the like, or foam such as Rohacell®, a polymethacrylimide—soldby Roehm Gmbh & Co., Darmstadt, Germany.

The core 16 can be cut or otherwise formed to a configurationcorresponding to the desired dimensions of the composite member 10. Inparticular, the ends of the core 16 can be formed (or machined) withoutthin portions that might be subject to breaking. For example, the core16 can define a substantially rectangular prismatic shape. In somecases, the core 16 can define acute or obtuse angles such that at leasta portion of the core 16 defines a tapering shape. For example, asillustrated in FIG. 1, the core 16 can define a truncated taperingportion at the periphery of the core 16. That is, a first side 34 of thecore 16 can be planar, a second opposite side 36 can be planar exceptfor an angled peripheral portion 38 that is angled toward the planedefined by the first side 34, and a transverse surface 40 can connectthe first and second sides 34, 36. The core 16 can be cut to the desiredconfiguration, e.g., using an ultrasonically reciprocating knife, or thecore 16 can be otherwise formed in the desired configuration. Typically,however, the core 16 is cut to a shape smaller than the entire space tobe defined between the sheets 12, 14, i.e., so that the sheets 12, 14are also configured to receive the laminate support member 20 in thetapering portion 22. Thus, a weak edge at the periphery of the core 16can be avoided, and instead the periphery of the core 16 can besupported by the support member 20.

The laminate support member 20 is also disposed between the laminatesheets 12, 14. In particular, one of the laminate support members 20 canbe provided at each end of the core 16. That is, four of the laminatesupport members 20 can be provided for a composite member having arectangular core, such as the core 16 illustrated in FIG. 1, with onesupport member 20 proximate each edge of the rectangular core 16.Alternatively, the support member 20 can be a continuous piece thatextends along two or more of the edges of the core 16. Each laminatesupport member 20 is typically configured to be disposed proximate thecore 16 so that the laminate support member 20 defines a rampdown ortaper corresponding to the tapering portion 22 of the laminate sheet(s).As illustrated in FIG. 1, the support member 20 is a wedge positioned atthe transition of the taper 22 where the laminate sheets 12, 14 aredirectly joined to fill the gap. The support member 20 is used where thesheet(s) 12, 14 change direction to separate and form an angle α.

Both sheets 12, 14 can diverge as shown in FIG. 2. The first side 34 ofthe core 16 defines an angled portion 35. FIG. 3 illustrates anembodiment in which the side 44 of the support member 20 is curved,i.e., to reduce slightly the angle α defined at the intersection of thefirst and second sheets 12, 14. The angled portion 38 of the core 16 canalso be curved.

In some cases, the core 16 can stop before the taper 22 so that theentire tapering space is filled with the support member 20. Thisapproach usually would add a small amount of weight to the panel becausethe support member outweighs the core. Further, the transverse surface40 of the core 16 can be disposed at other configurations than thatshown in FIGS. 1 and 2. For example, the transverse surface 40 candefine an obtuse angle β relative to the first side 34 of the core 16 asshown in FIG. 3.

As shown in FIG. 5, the support member 20 is a laminated compositematerial sufficiently thick to fill the space between the laminatesheets 12, 14 in the taper 22. The support member 20 can also be formedor cut to a size that is slightly greater than the size of the space to“overfill” the space. A support member that is slightly greater in sizethan the space may be designed to allow for differing compaction ratesduring cure, so that the final cured part does not have any undesirablesteps or mismatches in contour.

The support member 20 is typically stronger and stiffer than the core 16on a volumetric basis. In some cases, the support member 20 can have astrength that is between about 3 and 10 times as great as the strengthof an equal volume of the material of the core 16. The support member 20is often bonded to the core 16 with an adhesive 52, especially a foamingadhesive to fill any gaps or space between the support member 20 and thecore 16.

Reinforcement material 51 in the support member 20 is disposed in thedirection of a first axis (0°), and at an angle relative to the firstdirection, such as 45° clockwise relative to the first axis (+45), 45°counter-clockwise relative to the first axis (−45°), and/or 90°clockwise relative to the first axis (90°) in the various layers 50 a,50 b, 50 c. The ply orientation provides particular strength, stiffness,or thermal expansion characteristics. In FIG. 6, reinforcement fibers 51in the layer 50 a are disposed in a first direction (0°), and fibers 51in layers 50 b, 50 c are disposed at 45° and 90°, respectively. Acomposite noodle for filling a radius gap, and the formation ofcomposite members with directional properties, is further described inU.S. Pat. No. 6,562,436, which is incorporated by reference. The supportmember 20 corresponds to the noodle and functions in essentially thesame way.

If the support member 20 has a coefficient of expansion similar to thatof the laminate sheets 12, 14, stress induced by temperature changes isreduced.

The support member 20 can be cured separately from the laminate sheets12, 14 or in conjunction with the curing of the laminate sheets 12, 14.That is, according to one embodiment, the layers 50 of the supportmember 20 are assembled and cured, e.g., by compressing and heating thelayers 50. Thereafter, the cured support member 20 is disposed with thecore 16 between the uncured laminate sheets 12, 14, and the laminatesheets 12, 14 are cured. In this case, the sides 42, 44, 46 of thesupport member 20 can be prepared to promote adhesion between thesupport member 20 and the laminate sheets 12, 14 and the core 16. Forexample, the surfaces 42, 44, 46 of the support member 20 can beroughened by blasting, chemical etching, sanding, or the like.Alternatively, the layers 50 of the support member 20 can be disposed inthe uncured condition with the core 16 between the laminate sheets 12,14, and both the support member 20 and the laminate sheets 12, 14 can beco-cured in a combined operation. Alternatively, the layers 50 of thesupport member 20 can be disposed in the uncured condition with one orboth of the laminate sheets 12, 14, cured with the laminate sheet(s) 12,14, and then assembled with the core 16. If the support member 20 iscured without the core 16 being in place against the member 20, theconfiguration of the support member 20 can be maintained by using a toolor dam device against the support member 20. In any case, the adhesive52 can be provided to connect the support member 20 to the core 16.

FIG. 4 illustrates the lay-up of the composite member 10 according toone embodiment of the present invention, with the composite member 10shown in an expanded configuration for purposes of clarity. Thecomposite member 10 is positioned on a contoured surface 62 of a tool ormandrel 60.

The layers 30 of the first laminate sheet 12 are disposed on the mandrel60, and the core 16 and the support member 20 are disposed on the firstlaminate sheet 12. Two support members 20 are illustrated in FIG. 4, butany number of the support members 20 can be provided, typicallyaccording to the configuration of the composite member 10. Each supportmember 20 can be a unitary member or element and, in particular, a curedor partially-cured member. Alternatively, the layers of each supportmember 20 can be disposed separately and consecutively on the firstlaminate sheet 12. In either case, the adhesive 52 can be providedbetween the support member 20 and the core 16 to promote joining. Thelayers 30 of the second laminate sheet 14 are disposed over the core 16and the support members 20 so that the core 16 and support members 20are sandwiched between the laminate sheets 12, 14. Thereafter, a vacuumbag 64 can be disposed over the composite member 10. The resultinglay-up is then subjected to a curing operation that includes heating andcompressing the member 10. For example, in one typical operation, thecomposite member 10 is disposed in an autoclave, where it is heated to atemperature of between about 150° F. and 250° F. and subjected to apressure of between about 50 psi and 150 psi for an interval of betweenabout 30 minutes and 120 minutes. Thus, the layers 30 of the laminatesheets 12, 14, and optionally the layers 50 of the support member(s) 20,are cured in the desired configuration.

The support member 20 can be connected or engaged to the laminate sheets12, 14 so that the configuration of the support member 20 relative tothe sheets 12, 14 and core 16 is maintained, e.g., during the curingoperation. In some cases, an adhesive, such as a film adhesive, isprovided between the support member 20 and one or both of the sheets 12,14. An adhesive with a relatively low curing temperature can be used sothat the adhesive can be cured before the curing of the other componentsof the composite member 10. In addition or alternative to the use of anadhesive between the support member 20 and the sheets 12, 14, thesupport member 20 can be otherwise engaged with the sheets 12, 14, suchas with a mechanical connection. For example, as shown in FIGS. 2 and 3,a plurality of pins 70 (“z-pins”) can be disposed at least partiallythrough the sheets 12, 14 and the support member 20. The z-pins 70 canbe formed of various materials such as titanium or graphite, and aretypically rigid members that provide a mechanical connection between thesheets 12, 14 and the support member 20. In some cases, the z-pins 70are ultrasonically driven into the member 10. Z-pins and methods ofusing z-pins are further described in U.S. Pat. Nos. 4,869,770;5,685,940; 5,736,222; 5,876,540; 5,980,665; and 6,027,798, which areincorporated by reference.

The invention is not limited to the specific disclosed embodiments.Although specific terms are employed, they are used in a generic anddescriptive sense only and not for purposes of limitation.

1. A composite sandwich panel comprising: at least two laminate sheetsdefining a space in the form of a taper; and a laminate support memberfilling the taper.
 2. A composite according to claim 1 wherein thelaminate support member includes fiber reinforcement.
 3. A compositeaccording to claim 2 wherein the reinforcement is disposed in at leasttwo alternate directions in different plies.
 4. A composite according toclaim 1, further comprising an adhesive bonding the laminate supportmember to a core.
 5. A composite according to claim 1, furthercomprising a plurality of z-pins extending at least partially through atleast one of the laminate sheets and the support member.
 6. A compositemember formed by a process comprising: disposing a core on a firstlaminate; disposing a laminate support member on the first laminateadjacent the core; disposing a second laminate over the core andlaminate support member; and curing the first and second laminate suchthat the laminates define a taper with the laminate support member inthe taper.
 7. A composite member according to claim 6 wherein thelaminate support member has a plurality of layers of composite material.8. A composite member according to claim 6 wherein the laminate supportmember includes fiber reinforcement.
 9. A composite member according toclaim 8 wherein the reinforcement is disposed in at least two alternatedirections in different plies.
 10. A composite member according to claim6, further comprising an adhesive bonding the laminate support member toa core.
 11. A composite member according to claim 6, further comprisinga plurality of z-pins extending at least partially through at least oneof the laminate sheets and the support member.
 12. A composite sandwichpanel comprising: at least two laminate sheets defining a space in theform of a taper; a laminate support member filling the taper, whereinthe laminate support member includes fiber reinforcement that isdisposed in at least two alternate directions in different plies; anadhesive bonding the laminate support member to a core; and a pluralityof z-pins extending at least partially through at least one of thelaminate sheets and the support member.